Due at least in part to high crude oil prices, environmental concerns, and future availability, many internal combustion engine designers have looked to at least partially replace crude oil fossil fuels, e.g., gasoline and diesel, with so-called alternative fuels for powering internal combustions engines. Desirably, by replacing or reducing the use of fossil fuels with alternative fuels, the cost of fueling internal combustion engines is decreased, harmful environmental pollutants are decreased, and/or the future availability of fuels is increased.
One known alternative fuel is electricity. Many gasoline/electric powered hybrid vehicles and electric powered vehicles are known in the art. Electricity may be desirable as an alternative fuel because its use in powering an engine does not produce harmful exhaust emissions. Notwithstanding its advantages, electricity as a long-term partial or complete replacement of fossil fuels is unrealistic. For example, in order to replace the consumption of fossil fuels in vehicular internal combustion engines within the United States, 1 terawatt of electricity would be required. To meet the demands of 1 terawatt of electricity for powering automobiles, the current electricity output of the United States would need to be substantially increased. For various reasons, such as cost, such an increase is not physically and economically feasible. Also, the large batteries that typically power electric cars add significant weight to the vehicle, which affects the overall fuel economy of the vehicle. The range of electric cars can also be limited by the size and types of batteries used. Finally, the energy storage density of batteries is significantly lower than other alternative fuels, specifically ammonia. For at least the foregoing reasons, electricity is not a practical alternative fuel for replacing or supplementing crude oil fossil fuels for the powering of automobiles or other machines using internal combustion engines.
Another known alternative fuel is hydrogen. Unlike electricity, the United States possesses the capability of producing sufficient quantities of hydrogen to replace fossil fuels. Hydrogen can be produced using nuclear energy and renewable energy sources, such as wind and water, such that the production and use of hydrogen does not emit harmful carbon emissions to the environment.
Although hydrogen can be readily produced, its use as an alternative fuel has several drawbacks. For example, hydrogen has a low energy density by volume. For example, the energy density of hydrogen at 3,300 psi is about 7% of the energy density of gasoline. To travel the same distance on hydrogen compared to gasoline, the hydrogen tank would need to be approximately 14 times larger than most current gas tanks. Accordingly, vehicles operating on hydrogen would require storage tanks that are significantly larger than gasoline tanks. Further, hydrogen must be stored at high pressures, such as 10,000 psi, which can be relatively unsafe for distribution, handling and use. Additionally, tanks suitable for storing hydrogen at 10,000 psi must be very strong, such as 70 times stronger than ammonia storage tanks, and thus would be very expensive to manufacture. Hydrogen also is relatively explosive, which increases the danger associated with the distribution, handling and use of hydrogen.
Another known shortcoming with hydrogen as an alternative fuel is that the mass distribution of hydrogen to refueling centers across large geographical areas, such as the United States, is unfeasible. Hydrogen gas cannot be distributed using current pipelines used for distributing petroleum. Therefore, the only alternative would be to distribute the hydrogen by commercial trucking and railcar, which would result in a significant increase in the number of commercial trucks and railcars currently in use and thereby increase the overall energy required to distribute the hydrogen. Further, because hydrogen has a much lower energy density volume than gasoline, more hydrogen per volume would be needed at gas stations. Based on the storage capacity of current gas station storage tanks, the tanks would require more frequent refilling if hydrogen were stored instead of gasoline. Typically, gas stations are refilled with gasoline about once a day. In contrast, with hydrogen, stations would require refilling at least 12-15 times a day. Additionally, to decrease its volume, hydrogen may be stored as a cryogenic liquid. Accordingly, extra energy must be used to continually refrigerate the hydrogen liquid. Therefore, the storage of hydrogen as a liquid raises cryogenic concerns and wastes precious energy to store the hydrogen as a liquid. For at least these reasons, hydrogen is not a feasible alternative fuel for replacing or supplementing fossil fuels in powering internal combustion engines.
Yet other known alternative fuels are natural gas and propane. Although future quantities of natural gas and propane will be more readily available than other fossil fuels, such as crude oil, natural gas or propane as a fuel for powering internal combustion engines has several shortcomings. For example, natural gas and propane are fossil fuels and thus produce harmful carbon emissions and prices are forecast to dramatically increase along with petroleum. Also, the mass distribution problems associated with hydrogen are similar to the mass distribution problems of natural gas. Therefore, for at least these reasons, natural gas and propane are not feasible fuel alternatives for replacing or supplementing crude oil fossil fuels in powering internal combustion engines on a broad scale.
Hydrazine is another known alternative fuel capable of replacing or at least partially replacing crude oil fossil fuels. Hydrazine (N2H4) is a chemical compound widely used in rocket fuel. Although combustion of hydrazine produces no carbon emissions, is readily producible, has long-term availability, and is highly combustible, hydrazine has several drawbacks. For example, hydrazine is highly reactive, flammable and toxic. Accordingly, hydrazine is difficult to transport and handle and thus is not a feasible alternative to crude oil fossil fuels.
Ammonia is yet another known alternative fuel capable of replacing or at least partially replacing crude oil fossil fuels. Ammonia (NH3) is widely used in household cleaning supplies and agricultural fertilizer. Although liquid ammonia can cause injury if improperly used, such as being brought into contact with the skin or eyes, swallowed or inhaled, it is much less toxic and less dangerous to handle than many other alternative fuels. For example, unlike hydrogen, ammonia need not be stored under extreme pressures to maintain the ammonia at a usable energy density. Ammonia is currently manufactured and transported in mass quantities. Presently, ammonia is at least the fourth most transported commodity in the United States and costs less than gasoline, e.g., the cost of ammonia is less than that of gasoline per unit energy. Ammonia can be stored indefinitely as a liquid in a low pressure environment. Accordingly, ammonia can be transported via currently available high pressure pipelines. Therefore, the manufacture, handling and distribution of ammonia are more feasible than other known alternative fuels.
The energy density of ammonia at 150 psi is about 40% of the energy density of gasoline. In contrast to hydrogen, the ammonia tank need only be 2.4 times larger the gasoline tank to travel the same distance on ammonia as on gasoline. Further, if ammonia were distributed by current gas stations, the ammonia would have to be refilled only twice a day compared to 12-15 times per day as would be required for hydrogen.
Because ammonia does not contain carbon, the combustion of ammonia does not result in greenhouse gas, CO, CO2 or carbon particulate pollution emissions into the environment. More specifically, the byproducts of complete combustion of ammonia are relatively innocuous pure water and nitrogen. Further, ammonia can be readily manufactured using carbon-free energy sources, such as nuclear energy. Therefore, in some practical instances, little to no environmentally dangerous emissions are generated in the manufacture and combustion of ammonia.
Many ammonia-fueled internal combustion engines known in the art, however, suffer from one or more shortcomings. For example, ammonia has a slower flame speed, is more difficult to ignite, has a higher auto ignition temperature, and is less flammable than gasoline and many other alternative fuels, such as hydrogen. Some internal combustion engines use high compression ratios and supercharging to improve the combustibility of ammonia at high engine loads. However, at low engine loads, such as during idling of the engine, the combustibility of ammonia is incomplete and the performance of the engine suffers.
Some ammonia-fueled internal combustion engines known in the art use a combustion promoter to promote the combustion of the ammonia. These engines do not control or alter the ratio of ammonia to combustion promoter as the engine load and/or RPM changes to achieve stoichiometric operation of the engine. For example, many conventional ammonia-fueled engines do not use a closed loop control to adjust the amount of ammonia combusted in the engine based on one or more operating conditions during operation of the engine. Further, some conventional engines do not operate at, or are not concerned with the benefits of operating at, specific combustion conditions, such as rough limit, knock limit, or any particular condition between the rough and knock limits.
Based on the foregoing, there is a need for a spark ignited internal combustion engine capable of stoichiometric operation on ammonia and a combustion promoter throughout the entire range of engine loads and RPM.